When a person moves from a supine posture to a sitting or standing posture, pooling of blood in the abdomen and legs occurs due to gravity, which causes a diminished venous return to the heart, and therefore a diminished cardiac output and cerebral perfusion. Normally, the baroreceptors (pressure sensors in the wall of the carotid artery and aorta) sense the decrease in blood pressure and subsequently stimulate the sympathetic nervous system, causing a transient increase in heart rate of approximately 10 to 30 beats per minute. Due to the transient increase in heart rate, cardiac output and cerebral perfusion remains at a normal level. However, when the sensitivity of this baroreceptor reflex (also referred to as baroreflex) is reduced, there is an abnormal change in blood pressure and a diminished or absence of a transient increase in heart rate upon moving from a supine posture to a standing posture. In this case, blood pressure and cerebral perfusion substantially decrease upon moving from a supine posture to a sitting or standing posture, which can lead to a person feeling lightheaded, fainting or falling after standing up quickly.
The baroreceptor reflex and the ability to maintain blood pressure immediately after standing up deteriorate with age, causing symptoms including lightheadedness, confusion, nausea, and fainting. However, this orthostatic intolerance can also be asymptomatic. It is desirable to be able to routinely monitor heart rate changes when moving from a supine or lying posture to a sitting and/or standing posture, as this would enable the analysis of trends in the baroreceptor reflex under the natural conditions for standing up. It is thought that trend monitoring of the baroreceptor reflex and orthostatic intolerance could aid medical professionals in diagnosing underlying (chronic) disease, such as diabetes or heart failure. Timely detection of the deterioration of the baroreceptor reflex by a medical professional could facilitate intervention and potentially prevent falls and faints. Furthermore, monitoring trends in the baroreceptor reflex could be used to assess the effects of nutrition and medications that are known to improve or worsen orthostatic intolerance, such as salt and fluid intake, beta-blockers and anti-hypertensive drugs.
A reduced baroreceptor reflex may be assessed by a medical professional using various orthostatic stress tests during which blood pressure, heart rate and respiration rate are continuously monitored. Such tests include standing up, head-upright tilt (HUT) table testing, and the use of lower body negative pressure. However, such tests require visits to a medical facility, are generally not performed on a routine basis, are not standardized, and the results are often not repeatable. Furthermore, orthostatic stress tests, such as HUT are unnatural because the tilting of the patient does not resemble the real world scenario of the person standing up. In addition, the test considers a person that has been resting on a tilt table for some time (e.g., 15 minutes) at some point during the day, whereas it is preferable to evaluate orthostatic intolerance on a routine basis at a regular time in the morning, e.g. when getting up out of bed. Finally, orthostatic stress tests are clearly obtrusive and (mental) stress during the procedures influences the test results.
It is possible for a person to self-test using a blood pressure cuff and a heart rate monitor to measure the blood pressure and heart rate upon standing up from a sitting or supine position, but this is inconvenient and time consuming for the person. Furthermore, it is known that blood pressure measurements taken from a person in a lying position rely heavily on the exact position of the cuff, as well as the arm position. Such precise measurements cannot be expected from measurements taken in the home environment.
US 2007/0161912 describes the analysis of a baroreceptor reflex on standing up from a sitting or supine position using a device that includes a heart rate sensor and a posture sensor. However, this device needs to be implanted in the patient's body and requires a sensor to be placed in or around an artery or vein and/or electrodes to be attached to the patient's heart. Therefore, this device is not particularly suited to general usage by medical practitioners, and requires the patient to undergo a significant surgical procedure in order for the device to be implanted.
Other devices are known that can be used to detect the increase (or the absence of an increase) in heart rate upon standing and include devices that are placed in contact with the body, including a pulse oximeter or a heart rate watch, but these require the patient to remember to wear such devices, and may be uncomfortable to the patient while they are sleeping.
Therefore, there is a need for an apparatus and method for monitoring the baroreceptor reflex that can provide an indication of the baroreceptor reflex of the user using non-invasive and contactless measurements.